JP2014134635A - Control device of image forming apparatus, control method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an unnecessary radiation wave, prevent a negative ghost image, and prevent white gap according to an attribute of a non-image section.SOLUTION: A color image forming apparatus using electrophotography includes: means for generating an attribute signal which is an attribute of input image data to be printed and indicates a non-image section where a toner image is not formed or an image section where the toner image is formed; means which generates random data for generating micro light-emitting data at random; means which outputs the micro light-emitting data based on the random data according to the attribute signal; PWM modulation control means which generates a laser drive video signal by PWM-modulating the input image data when the attribute signal indicates the image section, or generates a laser drive video signal by PWM-modulating the micro light-emitting data when the attribute signal indicates the non-image section; and means which performs exposure by use of the generated laser drive video signal.

Description

  The present invention relates to a color image forming apparatus using an electrophotographic recording system such as a laser printer, a copying machine, and a facsimile, and more particularly, to minute light emission control of a non-image portion performed in order to obtain a higher quality image.

2. Description of the Related Art Conventionally, transfer-type color image forming apparatuses such as laser printers, copiers, and facsimiles using electrophotography have the following components.
A photosensitive member (photosensitive drum) as a plurality of first image carriers
・ Charging means for uniformly charging the photosensitive member to a predetermined polarity and potential ・ Exposure means (information writing means) for forming an electrostatic latent image on the charged photosensitive member
A developing unit that visualizes the electrostatic latent image formed on the photosensitive member with toner as a developer; a first transfer unit that continuously transfers multiple images onto an intermediate transfer belt that is a second image carrier; Second transfer means for transferring the four-color toner image formed on the intermediate transfer belt to the recording material. Fixing means for fixing the toner image on the recording material. The photoreceptor is an electrophotographic process (charging / exposure) repeatedly.・ Development, transfer, and fixing are applied for image formation.

  Here, the multicolor ghost phenomenon which is a problem in the conventional color image forming apparatus will be described.

  In the color image forming apparatus configured as described above, the primary transfer roller (voltage applying member) of the first transfer unit 205K of the K station 109 is not exposed to the own color (K) from the toner images of the previous stations 106 to 108. (See the enlarged view surrounded by the broken line in FIG. 10). By stepping on the primary transfer roller, a step remains on the photosensitive drum 201K even after charging (see FIG. 11A).

  When a latent image is formed in this state, the density is reduced by applying an offset corresponding to a step to the image portion after one full rotation of the photosensitive drum 201K, and a so-called negative ghost image is generated (see FIG. 9). ). This is a multicolor ghost phenomenon, and it goes without saying that such a phenomenon can occur not only in the K station but also in the M station and C station.

  Background exposure (hereinafter referred to as “BG exposure”) is known as a technique for preventing the multicolor ghost phenomenon. The BG exposure is a technique in which the charge amount of the station is increased in advance and the non-image portion is slightly emitted to return the increased charge amount to the conventional potential Vd after exposure ((b) in FIG. 11). See). According to the BG exposure, the non-image portion of the station including the portion corresponding to the image area of the previous station, which is the starting point of the multicolor ghost phenomenon, is finely exposed to such an extent that excessive toner adhesion does not occur. The offset on 201K is eliminated.

  Conventionally, in a color image forming apparatus, there is a problem that a so-called white gap phenomenon occurs in which an undesired white gap is left between images formed adjacent to each other in different colors. . This white-up phenomenon is caused by the formation of an electrostatic latent image, for example, an image edge portion, on which the drum surface potential changes sharply on the photosensitive drum. When this portion is developed by the developing means, a visible image becomes thinner than the original image. Arises from being done. It is already known that the above-described BG exposure is effective for improving the white gap phenomenon as well as the improvement of the multicolor ghost phenomenon.

  As a method for adjusting a minute light amount in BG exposure, for example, a method called a PWM (Pulse Width Modulation) method for changing a duty ratio of a pulse wave is known. In this case, the light emitting elements of the laser scanner emit light with a pulse width corresponding to a minute light emission amount in the non-image portion in addition to the image portion in synchronization with the image clock having a fixed frequency. (See Patent Document 1).

  A method for adjusting the bias current of a laser driving circuit is also known as another means for adjusting a minute light amount in BG exposure. This is because the first drive current corresponding to the image portion and the second drive current for minute light emission of the light emitting element are controlled, and the non-image portion emits the light emitting element with the second drive current, and the image portion The light emitting element emits light with a drive current obtained by adding the first drive current and the second drive current. (See Patent Document 2)

JP 2003-312050 A JP 2012-137743 A

  In the method of Patent Document 1, the entire surface of the non-image area in the print data is switched to minute light emission data generated randomly. However, even if most of the print area is white, the light emitting element emits a small amount of light over the entire non-image area, so even if the minute emission pulse width is varied based on a randomly generated pattern, the reduction in unnecessary radiation is reduced. It was not enough to do. Conventionally, so-called unnecessary radiation countermeasure members such as a shield, a filter, and a core are required to further reduce unnecessary radiated radio waves, leading to new problems such as cost increase, mounting area increase, and weight increase.

  The technique disclosed in Patent Document 2 has an effect that a stable image can be supplied against deterioration of the photosensitive drum, and the development bias or charging bias for each color can be shared to reduce the cost. However, in this method, the cost of the laser drive circuit and the power consumption of the entire apparatus are increased, and the image portion is also corrected. Therefore, it is technically necessary to adjust the light amount within a range that is not overcorrected due to environmental conditions. There was a drawback that it was difficult.

  Furthermore, in any case of the prior art, only a unique level of BG exposure control is performed for the non-image area below the density threshold, and the non-image area is not taken into consideration. That is, even if the same non-image part is a pure 'white' area where all other colors are white, if the other color is an image area even if the own color is white, the own color is white. However, there are cases where the other color is a character area, etc., but BG exposure control according to such attributes is not performed.

  Therefore, it can be said that there is still room for improvement in the appropriate adjustment of the amount of emitted light in the BG exposure of the non-image portion from the viewpoint of increasing the image quality required in recent color image forming apparatuses.

  The color image forming apparatus using the electrophotographic method according to the present invention is an attribute of input image data to be printed and is a non-image part that does not form a toner image or an image part that forms a toner image. Means for generating an attribute signal indicating, means for generating random data for generating minute light emission data at random, means for outputting the minute light emission data based on the random data in accordance with the attribute signal, When the attribute signal indicates the image portion, PWM modulation is performed on the input image data to generate a video signal for laser driving. When the attribute signal indicates the non-image portion, the minute light emission data is generated. PWM modulation control means for generating a laser drive video signal by performing PWM modulation, and means for performing exposure using the generated laser drive video signal And said that there were pictures.

  According to the present invention, in the BG exposure control, unnecessary radiated radio waves can be reduced, and negative ghost image generation and white gap suppression can be optimally realized according to the attributes of the non-image portion.

It is a schematic sectional drawing which shows the internal structure of the print engine part of a color image forming apparatus. It is a block diagram which shows the internal structure of a controller part. 2 is a block diagram showing an internal structure of a printer I / F that performs BG exposure control. FIG. It is a figure which shows an example of extended input image data. It is a figure explaining the operation | movement outline | summary of a PWM modulation control part. It is explanatory drawing of the operation example 1. FIG. It is explanatory drawing of the operation example 2. FIG. It is explanatory drawing of the operation example 3. FIG. It is explanatory drawing of a multicolor ghost phenomenon. It is explanatory drawing of a multicolor ghost phenomenon. It is explanatory drawing of background exposure.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing the internal structure of the print engine unit of the color image forming apparatus according to this embodiment. The print engine unit 101 in this embodiment is an in-line method in which photosensitive drums for each color are provided independently. However, it goes without saying that the present invention can also be applied to a copying machine having an image scanner unit added thereto, or a facsimile having a configuration added with a communication control unit for connecting to a public network. Although the description will be made on the assumption that a color image forming apparatus having an intermediate transfer belt is used, the present invention can also be applied to a color image forming apparatus adopting a method in which a toner image developed on a photosensitive drum is directly transferred to a transfer material. Needless to say.

  Hereinafter, in this embodiment, an inline having a plurality of photosensitive drums as the first image carrier and successively successively transferring multiple images onto the intermediate transfer belt as the second image carrier to obtain a full color print image. An explanation will be given taking a color image forming apparatus of the system as an example.

  The controller unit 102 plays a central role in system control, and an operation unit 103 and a printer controller 104 are connected. In response to an instruction from the operation unit 103, the controller unit 102 controls the print engine unit 101 to perform an image forming operation, and also performs communication with an external I / F.

  The operation unit 103 is an operation panel on which switches for various operations, an LED display, an LCD module, and the like are arranged.

  The printer controller 104 is a printer controller that sends YMCK-independent bitmap data from the controller unit 102 to the image exposure means 203Y, 203M, 203C, 203K as a laser drive video signal.

  The laser scanner unit 105 modulates and drives the semiconductor laser element in accordance with the laser drive video signal from the printer controller 104, and switches on / off the emitted laser light. The output laser light of each color scans the photosensitive drums 201Y, 201M, 201C, and 201K through an internal polygon mirror, an f-θ lens, and the like, and forms an electrostatic latent image. The laser scanner unit 105 includes image exposure means 203Y, 203M, 203C, and 203K.

  The intermediate transfer belt 110 is an endless endless belt, is suspended on a driving roller, a tension roller, an idler roller, and a secondary transfer counter roller, and rotates at a unique process speed in the direction of an arrow in the figure.

  Reference numerals 106 to 109 denote image forming stations. 106 forms yellow, 107 forms magenta, 108 forms cyan, and 109 forms black.

  Four photosensitive drums (201Y, 201M, 201C, 201K) in the image forming stations 106 to 109 are arranged in series in the moving direction of the intermediate transfer belt 110.

  The photosensitive drum 201Y is uniformly charged to a predetermined polarity and potential by the primary charging roller 202Y during the rotation process, and then subjected to image exposure by the image exposure unit 203Y. In response to the laser drive video signal from the printer controller 104, the image exposure unit 203Y scans the photosensitive drum 201Y to form an electrostatic latent image on the photosensitive drum corresponding to yellow.

  Thereby, an electrostatic latent image corresponding to the first color (yellow) component image of the target color image is formed. Next, yellow toner as the first color is attached to the electrostatic latent image by the yellow developer 204Y and developed. As a result, the image is visualized. In this way, a method in which toner is developed in a portion where an electrostatic latent image is formed by image exposure is referred to as a “reversal development method”.

  The yellow image formed on the photosensitive drum 201Y enters the primary transfer nip portion with the intermediate transfer belt 110. In the primary transfer nip portion, a voltage application member (primary transfer roller) 205Y is brought into contact with and in contact with the back side of the intermediate transfer belt 110. A primary transfer bias power source (not shown) is connected to the voltage applying member 205Y to enable bias application. The intermediate transfer belt 110 first transfers yellow at the port of the first color, and then sequentially transfers multiple colors of magenta, cyan, and black from the photosensitive drums 201M, 201C, and 201K corresponding to the colors that have undergone the above-described steps. The four-color toner images transferred onto the intermediate transfer belt 110 rotate and move in the direction of the arrow (clockwise) in FIG.

  On the other hand, the recording material P stacked and stored in the paper feed cassette 111 is fed by the paper feed roller 112, conveyed to the nip portion of the registration roller 113, and temporarily stopped. The recording material P once stopped is supplied to the secondary transfer nip by the registration roller 113 in synchronization with the timing at which the four color toner images formed on the intermediate transfer belt 110 reach the secondary transfer nip. Then, the toner image on the intermediate transfer belt 110 is transferred onto the recording material P by applying a voltage between the secondary transfer roller 114 and the secondary transfer counter roller.

  The recording material P onto which the toner image has been transferred is separated from the intermediate transfer belt 110 and sent to the fixing device 116 via the conveyance guide 115, where it is heated and pressed by the fixing roller and the pressure roller to receive the surface. The toner image is melted and fixed on. Thereby, a four-color full-color image is obtained.

  Thereafter, the recording material P is discharged from the paper discharge roller 117 to the outside of the apparatus, and one printing cycle is completed. On the other hand, the toner remaining on the intermediate transfer belt 110 without being transferred to the recording material P in the secondary transfer portion is removed by the cleaning unit 118 disposed on the downstream side of the secondary transfer portion.

  With the configuration as described above, development can be performed independently for each color of YMCK, so that a very high-speed color output image can be obtained by both copying and printing.

  FIG. 2 is a block diagram showing an internal configuration of the controller unit 102.

  The controller unit 102 prints print information (character code, etc.), form pattern information, macro instructions, and the like supplied from an external device (not shown) via an external I / F such as USB or Ethernet (registered trademark). The target image data (print data) is received. Thereafter, it has a function of performing predetermined image processing and outputting it to the print engine unit 101.

  The CPU 301 is a high-function processor that controls the controller unit 102 in an integrated manner, and includes an LSI in which the CPU and hardware circuits grouped in units of functional blocks are configured in the same package.

  The ROM controller 302 controls reading and writing of data with respect to the ROM 303.

  The ROM 303 stores a boot program for starting the OS of the controller unit 102 and a program for comprehensively controlling the controller unit 102.

  The secondary storage device control unit 304 controls reading and writing of data with respect to the secondary storage device 305.

  The secondary storage device 305 stores print data such as PDL (Page Description Language) data and image data for a secure job function, a BOX storage job function, and an interrupt printing function. The two-time storage device 305 is also used as an expansion buffer when transmitting / receiving data to / from an external information device.

  The image processing unit 306 performs reader-type image processing on the RGB digital image data output from the reader I / F 307. In addition, print image processing is performed on each color component signal of YMCK from raster data composed of character patterns, form patterns, and the like generated by the CPU 301 to generate independent bitmap data.

  A reader I / F 307 handles RGB digital image data between an image scanner (not shown) and the image processing unit 306.

  The printer I / F 308 handles YMCK output video data between the print engine unit 101 and the image processing unit 306. The printer I / F 308 includes a BG exposure control circuit described later.

  The I / F control unit 309 exchanges print data and the like between the external interface of the LAN I / F 310, the USB-D I / F 311 and the USB-H I / F 312 and the RAM 314.

  The LAN I / F 310 performs communication control with an external information device via the network, and receives print data.

  The USB-D I / F 311 performs communication control with an external information device via the USB, and receives print data.

  The USB-H I / F 312 controls a storage device that can be inserted and removed, such as a USB storage unit, a card reader that enables billing control and department designation control, an imaging device, and the like.

  The RAM controller 313 controls reading and writing of data with respect to the RAM 314.

  The RAM 314 functions as a main memory of the controller unit 102 and is also used as a work area related to image forming processing and a development area for image input / output processing.

  The system bus 315 is connected to the CPU 301 and the control units 302, 304, 306, 309, and 313, exchanges various register setting data and transmission / reception data, and includes a control signal, an address signal, and a data signal.

  FIG. 3 is a block diagram showing the internal structure of the printer I / F 308 that performs BG exposure control.

  The minute random data generation unit 401 generates image data (hereinafter referred to as “random data”) that is image data for performing minute light emission and whose value fluctuates randomly. The generated random data is used as a default pattern when performing minute light emission.

  The pulse width correction unit 402 corrects the pulse width of PWM modulation so as to change the minute light emission amount according to the density determination signal in the attribute signal (extended input image data) from the image processing unit 306. Here, the density determination signal is a color value for pixels in a region in which an image or a character is formed with a density value of a certain color component being 0 but a density value of a color component other than the certain color component being other than 0. This is a signal for identifying a region having a high pixel density and a region having a low pixel density.

  The pulse position correction unit 403 corrects the pulse position of the PWM modulation so as to change the minute light emission position according to the edge determination signal among the attribute signals from the image processing unit 306. Here, the edge determination signal is a color pixel for a pixel in a region where an image or a character is configured with a density value of a certain color component being 0 but other color components other than the certain color component being other than 0. It is a signal for identifying an edge portion whose density change amount is equal to or greater than a predetermined threshold.

  The selector 404 switches the output image data of the minute random data generation unit 401, the pulse width correction unit 402, and the pulse position correction unit 403 according to the region determination signal among the attribute signals from the image processing unit 306, Output the corrected minute emission data. Here, the area signal is a white area where the density values of all color components are 0, and the density value of a certain color component is 0, but the density values of color components other than the certain color component are other than 0, and the image Or it is a signal which identifies the area | region where the character is comprised.

  The PWM modulation control unit 405, based on the non-image portion determination signal that identifies the non-image portion that does not form a toner image, among the attribute signals from the image processing unit 306, is input image data from the image processing unit 306 or after correction. PWM modulation is performed on minute light emission data. For example, in an area where an image is present in the station (area where the density value is other than 0), PWM modulation is performed on the input image data using the first LUT to obtain a laser driving video signal. On the other hand, in an area where there is no image in the station (area where the density value is 0), a second LUT different from the first LUT is used for the corrected minute emission data so as not to cause toner adhesion. PWM modulation is performed to obtain a laser drive video signal.

  Next, the operation of the color image forming apparatus according to this embodiment will be described.

  First, the CPU 301 of the controller unit 102 receives print data supplied from an external device (not shown) via the USB-D I / F 311 and the LAN I / F 310 and stores the print data in the RAM 314.

  A rendering control unit in the CPU 301 creates raster data including a corresponding character pattern, form pattern, and the like from the input print data, and transfers the raster data to the image processing unit 306. At this time, the rendering control unit displays a determination bit 1 for determining whether or not the print data exists, and a determination bit 2 for determining whether the area is an image area or a character area when the print data exists. Add to the data. In this embodiment, when the determination bit 1 is “0”, it is “an area without print data”, and when it is “1”, it is an “area with print data”. When the determination bit 2 is “0”, “print data is a character area”, and when “1” is “print data is an image area”.

  Next, the image processing unit 306 performs input masking processing for conversion to a standard color space that does not depend on the device, and the LOG conversion unit converts a RGB luminance signal into a CMY density signal using a lookup table or the like. At this time, the image processing unit 306 adds a determination bit 3 for determining whether the color pixel density amount is equal to or greater than a predetermined threshold when generating the YMCK density signal. In this embodiment, when the determination bit 3 is ‘0’, the area is a “print data density low area”, and when the determination bit 3 is ‘1’, the area is a “print data density high area”.

  In the line delay memory, the black component signal is extracted by delaying the line by a period for generating the UCR control and filter control signals.

  The gamma correction unit corrects the gamma characteristic of the print engine unit 101, and performs edge enhancement and smoothing processing using an output filter. At this time, the image processing unit 306 adds a determination bit 4 for determining whether or not the change amount of the color pixel density is equal to or greater than a predetermined threshold value during the edge enhancement / smoothing process. In this embodiment, when the determination bit 4 is “0”, “no edge portion in the print data” is set, and when “1”, the print data has an edge portion.

  Then, for each pixel of YMCK bitmap image data, data correction is performed with reference to the determination bits 1 to 4 for a pixel whose value (pixel value) is ‘0’ (white).

  First, depending on whether the pixel value is other than “0” or “0”, the value of the extended input image data (D4 in FIG. 4) to be transferred to the printer I / F 308 is switched. As shown in FIG. 4, if the pixel value is other than “0”, it is recognized that there is an image portion (hereinafter referred to as “image portion”) that forms a toner image for the station of that color, and D4 is set. '1' is set ((1) in FIG. 4). On the other hand, if the pixel value is “0”, the station of that color is recognized as having no image portion (non-image portion), and “0” is set in D4 ((2) to (8) in FIG. 4). ).

  For a pixel (D4: 1) having a pixel value other than “0”, since the station of that color has an image portion, values of input image data to be transferred to the printer I / F 308 (D3 to D0 in FIG. 4). ) Contains the value of the bitmap image data as it is ((1) in FIG. 4). In this embodiment, the input image data is 4-bit data, but the data length is not limited to this and is arbitrary.

  For a pixel (D4: 0) having a pixel value of “0”, since there is no image portion in the station of the color component, data correction is performed with reference to determination bit 1 and determination bit 2.

  Specifically, when the pixel value is “0” and the determination bit 1 is “0”, D3 of the input image data is “0”, and D2 has an arbitrary value. Thus, this pixel is recognized as a complete white area (FIG. 4 (2)).

  When the pixel value is “0” and the determination bit 1 is “1”, D3 of the input image data is “1” (FIGS. 4 (3) and (4)).

  Further, in this case, referring to the determination bit 2, in the case of “1”, D2 is set to “1”, and an arbitrary value is entered in D1. As a result, the pixel is recognized as white in color and the background is an image area ((3) in FIG. 4).

On the other hand, with reference to the determination bit 2, in the case of “0”, D2 is set to “0” and an arbitrary value is entered in D1. As a result, this pixel is recognized as having a white color and a background being a character area ((4) in FIG. 4).
In this embodiment, when the color is white and the background is an image or a character area ((3) and (4) in FIG. 4), the determination bit 3 and the determination bit 4 added in the image processing unit 306 are set. Refer to it for further data correction.

  Specifically, referring to determination bit 3, in the case of “1”, D1 is “1” in the input image data, and this pixel is a region having a white color and a high background density. (5 in FIG. 4).

  On the other hand, referring to the determination bit 3, in the case of “0”, D1 is “0” in the input image data, and this pixel is recognized as a region having a white color and a low background density. (FIG. 4 (6)).

  Further, referring to the determination bit 4, in the case of “1”, D0 is “1” in the input image data, and this pixel is an area where the color is white and the edge is detected in the background. ((7) in FIG. 4).

  On the other hand, referring to the determination bit 4, in the case of “0”, D0 is “0” in the input image data, and this pixel is an area where the color is white and the edge is not detected in the background. It is recognized ((8) in FIG. 4).

  In this way, the bitmap image data of each YMCK subjected to the conversion process is temporarily stored in the RAM 314 via the CPU 301 in the data format of the extended input image data and the extended input data in total 5 bits (D4 to D0 in FIG. 4). Accumulated.

  Next, the printer I / F 308 takes bitmap image data from the RAM 314.

  In order to generate a laser driving video signal output to the print engine unit 101, the printer I / F 308 performs the following control.

  First, the PWM modulation control unit 405 performs the first look-up table (LUT1) under the condition that the station has an image portion, that is, the condition that D4 of the extended input image data is “1” ((1) in FIG. 4). Select. Then, PWM modulation is performed according to the values of D3 to D0 of the input image data to obtain a laser drive video signal ((a) in FIG. 5).

On the other hand, the second look-up table (LUT2) is selected under the condition that the station does not have an image portion, that is, the extended input image data D4 is “0” ((2) to (8) in FIG. 4). Then, according to the minute light emission data determined by the values of D3 to D0 of the input image data, PWM modulation is performed to such an extent that toner adhesion does not occur, and a laser driving video signal is obtained (FIGS. 5B and 5C). ))
Here, as described in FIGS. 5A and 5B, the minimum width of the BG exposure clock used in the LUT 2 is smaller than the minimum width of the image clock used in the LUT 1. It is necessary to have a pulse width that does not cause the problem. Therefore, the frequency of the PWM modulation clock of LUT2 must be larger than that of LUT1. In this embodiment, the frequency of the PWM modulation clock for LUT1 is 16 times that of the image clock for 600 dpi-1 pixels, whereas the frequency of the PWM modulation clock for LUT2 is 64 times. However, the multiplication factor is not limited to this.

  The minute light emission data for LUT2 is controlled as follows.

  First, the minute random data generation unit 401 internally generates random data so that the data after PWM modulation becomes a random pattern described in FIG. Specifically, a value from 00h to 0fh is randomly generated, and the LUT 2 is controlled so as to slightly change the pulse width and pulse position of the minute emission data based on the random data.

  The pulse width correction unit 402 changes the pulse width of the minute light emission data according to the density determination signal (determination bit 3, extension input data D1) under the condition that D4 of the extended input image data is “0”. Specifically, as shown in FIG. 5B, when the density determination signal is “1”, the pulse width is larger than that of “0”, and the minute light emission amount is controlled by the background density. To do. When the density determination signal is “1”, in the case of FIG. 5C, the random data of the minute random data generation unit 401 passes through 0 to 0 fh, and the random data of 00 to 07 h is converted to 08. Convert to ~ 0fh. As a result, control is performed so that only 08 to 0 fh is used from random data. On the other hand, when the density determination signal is “0”, in the case of FIG. 5C, the random data of the minute random data generation unit 401 passes through 00-07h, and the random data of 08-0fh. Is converted to 00-07h. As a result, control is performed so that only 00 to 07h is used from random data.

  The pulse position correction unit 403 changes the pulse position of the minute light emission data according to the edge determination signal (determination bit 4, extended input data D0) under the condition that D4 of the extended input image data is “0”. Specifically, when the edge determination signal is “1” from the complete white area ((2) in FIG. 4), it is recognized that “there is an edge on the left side”. Conversely, when the edge determination signal is “1” from the image area or the character area ((3) and (4) in FIG. 4), it is recognized that “there is an edge on the right side”.

  Then, when it is recognized that “there is an edge on the left side”, control is performed so that 07 h or 0 fh is fixedly selected from the output random data of the pulse correction unit 402. Then, as shown in FIG. 5C, the minute exposure position is fixed on the edge detection side (here, the right side).

  On the other hand, when it is recognized that “there is an edge on the right side”, control is performed so that 00h or 08h is fixedly selected from the output random data of the pulse width correction unit 402. Then, as shown in FIG. 5C, the minute exposure position is fixed on the edge detection side (here, the left side).

  When the edge determination signal is “0”, it recognizes “no edge detection” and passes through the output data of the pulse width correction unit 402 as it is.

  The output terminals of the minute random data generation unit 401, the pulse width correction unit 402, and the pulse position correction unit 403 are connected to the input terminal of the selector 404 (IN1, IN2, IN3). These data are switched according to the region determination signal (determination bit 1 and determination bit 2, extension input data D3 and D2) under the condition that D4 of the extended input image data is “0”, and PWM is used as minute light emission data. The result is output to the modulation control unit 405.

  The laser driving video signal generated by the PWM modulation control unit 405 is sent to the image exposure unit 203 via the printer controller 104, and an image is formed on the recording material independently of YMCK.

  With the printer I / F 308 configured as described above, the non-image portion microexposure algorithm in this embodiment operates as follows.

(Operation example 1)
The following control is performed for the areas where the density values in the second, third, and fourth stations (107, 108, and 109) are 0 (areas A, B, and C in FIG. 6).

  When the region A is determined ((2) in FIG. 4), the output of the selector 404 is masked by the region determination signal (determination bit 1 and determination bit 2, extended input data D3 and D2) in the input image data. Stop the microexposure algorithm.

  On the other hand, the regions B and C ((3) and (4) in FIG. 4) use random data defined by default, that is, the output data (IN1) of the minute random data generation unit 401 to execute the minute exposure algorithm. Make it work.

(Operation example 2)
The following control is performed for the areas where the density value is 0 (areas A, B, and C in FIG. 7) in the images of the second, third, and fourth stations (107, 108, and 109).

  Regions B and C ((5) and (6) in FIG. 4) are output using the output data (IN2) of the pulse width correction unit 402 in which the minute light emission amount is controlled by correcting the minute pulse width by the density determination signal. Operate the microexposure algorithm. Alternatively, in the regions B and C, the minute exposure algorithm is operated by switching the output data (IN1) of the minute random data generation unit 401 and the output data (IN2) of the pulse width correction unit 402 by the density determination signal.

(Operation example 3)
The following control is performed for the areas where the density values in the second, third, and fourth stations (107, 108, and 109) are 0 (areas A, B, and C in FIG. 8).

  Regions B and C ((7) and (8) in FIG. 4) are output using the output data (IN3) of the pulse position correction unit 403 in which the minute light emission amount is controlled by correcting the minute pulse position using the edge determination signal. Operate the microexposure algorithm. Alternatively, in the regions B and C, the minute exposure algorithm is operated by switching the output data (IN1) of the minute random data generating unit 401 and the output data (IN3) of the pulse position correcting unit 403 by an edge determination signal.

  As described above, according to the present embodiment, in the digital BG exposure performed by PWM modulation, optimal BG exposure control according to the attribute of the non-image part can be performed. Therefore, it is possible to optimally realize the reduction of unnecessary radiated radio waves, the prevention of the negative ghost image and the suppression of the white gap.

(Other embodiments)
The object of the present invention can also be achieved by executing the following processing. That is, a storage medium that records a program code of software that realizes the functions of the above-described embodiments is supplied to a system or apparatus, and a computer (or CPU, MPU, etc.) of the system or apparatus is stored in the storage medium. This is the process of reading the code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention.

Claims (9)

Means for generating an attribute signal indicating the attribute of the input image data to be printed and indicating whether the image portion is a non-image portion that does not form a toner image or an image portion that forms a toner image;
Means for generating random data for generating minute emission data at random;
Means for outputting the minute emission data based on the random data according to the attribute signal;
When the attribute signal indicates the image portion, PWM modulation is performed on the input image data to generate a video signal for laser driving. When the attribute signal indicates the non-image portion, the minute light emission data is generated. PWM modulation control means for generating a laser drive video signal by performing PWM modulation on the device,
Means for performing exposure using the generated video signal for laser driving;
A color image forming apparatus using an electrophotographic system. A white area where the density values of all color components are 0, and an area where the density value of a certain color component is 0 but the density values of color components other than the certain color component are other than 0, and an image or character is configured Including an area determination signal for identifying
The means for outputting is based on the region determination signal,
When the pixel of the input image data is the white region, the minute emission data is not output,
2. The color image forming apparatus according to claim 1, wherein when the pixel of the input image data is an area where the image or character is formed, the minute light emission data is output. The attribute signal includes a density determination signal for identifying a high density area and a low density area in the input image data,
The color image forming apparatus according to claim 1, further comprising a unit that corrects a pulse width of the PWM modulation according to the density determination signal.   The density determination signal indicates that the density value of a certain color component is 0, but the density value of a color component other than the certain color component is other than 0, and among the pixels in the area where the image or character is configured, the color pixel density 4. The color image forming apparatus according to claim 3, wherein when the amount is equal to or greater than a predetermined threshold value, the area is a high density area. The attribute signal includes an edge determination signal for identifying an edge portion in the input image data,
Means for correcting the pulse position of the PWM modulation according to the edge determination signal;
The color image forming apparatus according to claim 1, wherein the color image forming apparatus is a color image forming apparatus.   The edge determination signal indicates that the density value of a certain color component is 0, but other color components other than the certain color component are other than 0, and the color pixel density of pixels in an area in which an image or a character is formed. 6. The color image forming apparatus according to claim 5, wherein an edge portion is formed when the amount of change is equal to or greater than a predetermined threshold value.   7. The table according to claim 1, wherein the PWM modulation control means uses different tables for performing PWM modulation on the input image data and performing PWM modulation on the minute light emission data. 2. A color image forming apparatus according to item 1. Generating an attribute signal indicating the attribute of the input image data to be printed, which indicates whether it is a non-image part that does not form a toner image or an image part that forms a toner image;
Generating random data for randomly generating minute emission data; and
Outputting the minute emission data based on the random data in accordance with the attribute signal;
When the attribute signal indicates the image portion, PWM modulation is performed on the input image data to generate a video signal for laser driving. When the attribute signal indicates the non-image portion, the minute light emission data is generated. PWM modulation control step for generating a laser driving video signal by performing PWM modulation on the
Performing exposure using the generated laser driving video signal;
A color image forming method using an electrophotographic system characterized by comprising: A program for causing a computer to function as the color image forming apparatus according to any one of claims 1 to 6.